Biodegradation & Composting

What Happens to Bioplastics at Industrial Composting Sites?

What happens to compostable plastics at an industrial composting plant? You want the truth, the whole truth and nothing but the truth ... including the pictures and videos? The article of the year brought to you by

On the 16th of June 2020, I visited a composting facility in Flanders (Belgium) called Ecowerf to find out what happens to compostable plastics in reality.

I had the pleasure to Meet Dirk Verbruggen who’s the person in charge of the composting operations at the Ecowerf site. Dirk is an International expert when it comes to testing compostable materials. Dirk is a great source of knowledge and know-how.

Dirk Verbruggen
Dirk Verbruggen, Composting Operations, Ecowerf

Here’s a summary of our very interesting conversation.

Composting vs Fermentation

There are two types of industrial facilities that process organic waste: composting and fermentation facilities. Composting produces compost; fermentation produces biogas and digestate.

Compost will be sold to farmers, companies or individuals. Biogas will be converted into electricity or biofuels, and digestate will be sold to farmers as fertiliser or send to composting facilities.

Both composting and fermentation processes are done by bacteria and micro-organisms: the bacteria eat and digest the waste.

There’s no need to add bacteria at a composting facility; the bacteria are present in the organic waste. A new fermentation facility needs to receive “new” digestate from another fermenting plant to start operations.

The composting of organic waste is an aerobic process; oxygen is needed and is added during the composting process. Fermentation is an anaerobic process, it doesn’t need oxygen and no oxygen is added during the process.

During the composting of GFT (domestic organic waste), biogas is emitted but not collected by the composters. Composters may use pre-fermentation installations to collect that biogas.

Biogas can be burned directly by an engine to generate electricity or needs additional processing to be converted into biofuels. Making biofuels is more expensive than generating electricity.

Industrial Composting at Ecowerf

Ecowerf is an industrial composting facility located in Leuven, Flanders (Belgium). The plant processes 47.000 tonnes organic waste and produces 16.000 tons compost per year. The conversion rate of composting is one third. One third of the biomass will be converted into compost; one third is water and one third is residue that will be re-composted or used as biomass.

The composting operations at Ecowerf involves around 10 employees.

Composting facilities are audited every year by several control-organisms to ensure best practices are applied. Several conditions have to be respected to produce healthy and high-quality compost.

The composting method of Ecowerf consists of 4 phases: pre-treatment, composting, post-treatment and maturation. It’s an aerobic and in-door (closed) process.

A good composting process needs air / oxygen (forced aeration), water, temperature, and a good Ph-level.

Bacteria need high temperatures, humidity, oxygen and time. An average composting process takes around 10 to 12 weeks (4 phases).

Sick plants are also delivered to the composting facilities. Therefore, we need high temperatures to avoid compost contamination with bad pathogens. The organic waste needs to rest at least 4 days at 60 °C or 10 days at 55°C for hygienisation (to destroy diseases and weedseeds).

Industrial composting
The organic waste is delivered here by the trucks.

The Composting Journey starts ….

Video of the Composting Hall where the “composting phase” takes place.

Compost ready to be sold.
Compost residue
Residual waste removed from the compost. This contaminates the compost. Many plastic bags.

Here’s the video …

Residue composting
Residue of the composting process. The white bits are plastic films.

Organic Waste Streams

  • GFT

In Belgium, domestic organic waste is referred to as GFT (Groente, fruit en tuinafval – Vegetable, Fruit and Garden waste). Today, GFT is sorted and collected separately. This is the largest input stream for Ecowerf.

  • OBA

Corporate organic waste is referred to as OBA (Organisch Biologisch Afvalstoffen – organic biological waste). This includes the corporate (office) GFT + industrial organic waste and by-products. Corporate GFT is not yet collected separetly. However, hotels, restaurants and catering serving more than 50 warm meals per day will have to sort their organic waste as from 2021 to enable separate collection.

  • Roadside grass

Grass, branches and leaves from public domain.

  • Compostable materials

Including compostable plastics. Ecowerf processes around 1 million compostable plastic bags per year. Other objects include cups, cutlery and packaging mostly with the OK home compost label.

The actual composting (phase 2) happens in the compost hall. Other compostable materials that are treated in the composting plant are PLA, cardboard, sugercane, bagasse, palm leaves, wood, paper, cellulose, Mater-bi, bran, husk and avocado pitts.

  • Festivals

Festival organisers need to contact the local authority and local industrial composters to ask for authorisation to use specific compostable tableware (cups, plates, cutlery) if they want to process their “disposable” packaging at the composting facility.

One of the most important problems when it comes to processing festival “disposable” packaging is contamination from residual waste.

Where should we send the organic waste?

Should organic waste be sent to composting or fermentation facilities?

The location of the facilities and the collected waste play a role in this equation due to the (environmental) cost of transport.

However, there may be some principles.

  • Kitchen waste

It may be wiser to send kitchen waste (including meat and fish waste) to a fermentation plant to have it converted into electricity. The animal fats have more “energy” than garden waste.

  • Garden Waste

Garden waste, gras and branches should be sent to composting facilities.

  • Paper and Cardboard

Clean paper and cardboard should be sent to a paper recycler. Composting facilities send the ‘clean paper’ it receives to the paper recyclers.

Contaminated paper and cardboard (with food residue for instance) should be sent to composting facilities not to the paper recyclers.

Corona Crisis

There was much more domestic organic waste during the corona confinement and the level of contamination with residual waste was much higher than usual.

Compostable Plastics

Some of the materials and objects tested by Dirk over the years.

There’s no point in sending compostable plastic bag to fermentation facilities for convertion into biogas as compostable plastic bags have no energy. Paper bags are more interesting for fermentation as they have more “energy” than compostable plastic bags.

Composters are not interested to process compostable plastics at their facilities as they receive enough organic waste. Accepting compostable plastic is perceived as “opening the door” to more waste stream contamination.

Remember, It’s (visually) impossible for customers to differentiate between regular and compostable plastics. The risk of contamination starts at the sorting and collection.

A compostable plastic should first be sent to the composting facility for testing before it can eventually be authorised for composting.

Compostable plastics certifications and standards” are based on lab conditions but do not reflect the composting reality.

Compostable plastics are probably tested in powders with artificial conditions such as stable temperature, or unstacked cups for instance. These conditions do not occur in reality.

Experience has thought us that “compostable plastic certification” have no value in the field. Some “certified” compostable plastics will not biodegrade while some “uncertified” compostable plastics may biodegrade.

If you want to be sure: have it tested at the composting facility where it’s supposed to be processed after use.

  • Compostable Plastic Bag

The thickness of the bag is determinant. Thin bags will disappear during composting. There were problems in the early days of compostable plastic bags, but the problems seem to be solved. Today, these bags are necessary for the collection of domestic organic waste (GFT) and are processed without any problems at the composting facilities.

  • PLA

PLA is usually not liked and not welcomed by industrial composters. It takes too long for PLA to degrade. No composting facilities will accept and compost PLA in Belgium.

PLA cannot be added with the PMD waste stream intended for recycling because it will contaminate the recycling process.

Whether the PLA has a “compostable plastics logo” or not it doesn’t make a difference. Compostable plastic certifications have no value in the eyes of the industrial composter. Industrial composters want to test it themselves.

When PLA is used with other compostable materials and it’s in small quantity it may compost on time. Thin PLA lining in cups and containers may disappear, but if the layer is too thick it will contaminate the compost.

  • PBAT

The Ecovio from BASF takes too long to compost. In addition, there are little balls that look like styrofoam in the residue.

pbat ecovio basf composting
Ecovio from BASF. Results after 7 weeks of composting. It hasn’t degraded yet.
compostable agricultural mulch film
Compostable agricultural mulch film doesn’t turn into compost after 5 weeks of composting.
  • Cutlery

Cutlery made from compostable plastic will not be accepted as they don’t biodegrade. They’re too thick.

  • Coffee capsules, Tea Bags and Fruit sicker

These items, even if they’re certified as compostable plastic should not be included in the domestic waste stream as they do not biodegrade. They contaminate the compost. Same applies for PLA coffee capsules.

Fruit sticker contamination compost
A fruit sticker contaminating the final compost.

Future Concerns

Today, compostable plastics represent a minor share of the domestic organic waste stream. Should compostable plastics become mainstream, it may cause a problem in terms of concentration or “mono stream”. Good and healthy compost needs a healthy mix of organic waste streams.

More analysis and research is needed regarding the impact of “compostable plastic compost” on the soil. Compostable plastics may not improve the quality of the compost or soil. What is the effect on the germination, root system and micro-organisms living in the soil?

We should also look at the “sustainability” of the feedstock used to produce compostable plastics. Good example are FSC paper, Fair Trade Palm leaves, etc.

EU norms such as “EN 13432 norm” should be based on the reality of composting facilities instead of lab test conditions.

More Pictures

industrial composting pla packaging
The frame degrades, the transparent PLA films doesn’t.
Example of packaging that degrades. Thin PLA lined.
None of these PLA cups degrade. The composters refuse them.
All these cups degrade and are accepted at the composting plant. Most are made from paper with a thin bioplastic layer inside.
None of these (compostable plastic) cutlery degrade. They’re too thick.
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